Hi I am Pharmacist and have just checked with the BNF for Children which is the standard reference for children's medicines, which recommends that children between 1 month and 2 years can be given 2.5ml twice a day. Daktarin is not licensed in children under 4 months.This will be the reason that the leaflet say not for under 4 months. I have checked the license information and it does not give the reason for this so it may simply be that trials have not been carried out in such young babies. For it to be in the BNF it will have been used widely in young babies. I hope this reassures you.